1. Field of the Invention
The present invention relates to a high pressure fuel pump, and more particularly, to a high pressure fuel pump for increasing a fuel pressure supplied to an internal combustion engine.
2. Description of the Related Art
As a high pressure fuel pump, there is a conventionally known plunger pump which pressurizes a fuel by a plunger sliding in a cylinder. In such a plunger pump, if a gasoline having a relatively low viscosity as the fuel, a fuel leaked from a clearance between the cylinder and the plunger enters into a mechanical sliding portion which reciprocates the plunger through a driving shaft. Therefore, since the mechanical sliding portion can not be lubricated using grease or oil, a product in which the mechanical sliding portion is lubricated by gasoline has become commercially practical. However, a product in which the gasoline is used as a lubricant does not have sufficient mechanical efficiency and durability.
High pressure pumps which have overcome the above described problem are described in Japanese Patent Applications Laid-open No.8-232850 and No.7-12029.
The former publication discloses an axial swash plate bellows type fuel pump in which a thrust bearing is mounted to an inclined brim portion of a rotating shaft to form a swash plate, and a plurality of pump chambers constituted by bellows are sequentially expanded and contracted by rotating the swash plate, thereby pressurizing the fuel supplied into the pump chambers. According to this prior art, since the pump chamber is constituted by the bellows, it is possible to prevent the fuel from leaking from the pump chamber.
The latter publication discloses a technique in which in order to prevent a fuel leaked from a sliding clearance between a piston and a cylinder of a high pressure fuel pump from entering into a grease charged in a bearing, a needle bearing and the like, a diaphragm is provided between a chamber accommodating the piston and the cylinder and a chamber accommodating the needle bearing and the like, thereby liquid-tightly sealing both the chambers.
However, in the technique disclosed in the former publication in which the pump is constituted by the bellows, a high pressure is directly applied to the bellows and therefore, there is a problem that the bellow must be made of metal having a high pressure resistance, which is expensive.
In the conventional technique disclosed in the latter publication, if the pump has a single cylinder, the operation of the diaphragm is a simple vertical movement and there seems to be no special problem. However, in the case of a high pressure fuel pump, in order to reduce a discharge pulse, the pump has a plurality of plungers and is formed into an axial plunger shape in general. In this case, if a seal diaphragm is provided for every plunger, its size is increased and is not practical. In order to avoid this problem, if the plurality of plungers is sealed by a single diaphragm, there is a problem that a motion of the diaphragm at the time of operation of the plungers is partially varied, which largely deteriorates the durability of the diaphragm.